1. Field of The Invention
This invention relates to an image processing system for performing a processing such as a tone correction on image data obtained by optically reading a picture or the like and thereafter outputting processed image data.
2. Description of The Related Art
In recent years, with advance of image processing techniques, an image processing system, which can read image data of a picture or the like and perform various processings on the image data and edit the image data by, for example, "pasting" or placing an image represented by the image data on a document, has come to require a variety of functions and an improvement in operability.
A conventional image processing system has a function of a tone correction, by which a tone of read image data is converted into another tone arbitrarily indicated by an operator. In such a case, a desired correction rate or degree can be set by first displaying a curve graph (hereunder sometimes referred to as a tone curve or as a tone correction curve), in which tone levels (namely, densities) of input image data are plotted in abscissa (namely, in horizontal axis) and tone levels of output image data obtained by performing a tone correction on the tone of the input image data are plotted in ordinate (namely, in vertical axis), as illustrated in FIG. 10 and next modifying the tone curve by using an input means such as a mouse. In case of FIG. 10, a tone curve 1 corresponds to a case where a tone level of output image data is equal to a tone level of corresponding input image data (namely, output image data is obtained from input image data without any conversion or modification). Further, as shown in FIG. 10, a tone curve 2 is entirely lower than the tone curve 1. Thus, in case of employing the tone curve 2, an output image represented by the output image data is lighter than an input image represented by the input image data. In contrast, a tone curve 3 is entirely higher than the tone curve 1. Thus, in case of employing the tone curve 3, an output image represented by the output image data is darker than an input image represented by the input image data. Further, a portion of an output image, which is represented by tone levels of a steep portion of a tone curve, is enhanced in comparison with a corresponding input image. Conversely, another portion of the output image, which is represented by tone levels of a gentle portion of the tone curve, is blurred or scumbled in comparison with the corresponding input image.
Incidentally, as above described, the setting of a tone curve can be freely performed by an operator according to uses of image data (namely, purposes for which the image data is used). However, in case where an original or input image (hereunder sometimes referred to as a draft) is a photograph, densities of the original image vary with a subject (namely, an object to be photographed), conditions of a photographing thereof and conditions of development of a film. It is, therefore, necessary for obtaining an output image, which is most suitable for uses thereof, to set a tone curve for each draft.
However, in case where a tone curve is set by the conventional image processing system with the intention of a tone correction, an operator is compelled to measure densities of pixels of an original image by using, for instance, a densitometer and repeat trial settings of a tone curve in view of a distribution of measured densities in the original image. Such an operation calls for wide experience and great skill. Thus, it is highly required for an image processing system to have a function, by which operability of setting a tone curve is improved.